A woman's face, or the woman who possesses such a face, that is a highly suitable recipient for a man's semen/ejaculation, i.e., an acronym for Blow A Load On Face. A woman with such a quality, particularly with interest and/or enthusiasm for the act, is for many men the holy grail of mating.

Meant in a flattering sense as opposed to misogynistic, considering that blowing your load on a beautiful face is one of the more sublime experiences in a man's life.

man 1: BALOF alert! <indicates hot chick>
man 2: Aww, yeahh.

or

man 1: Now, what you got right there is a balof, is what you got right there.
man 2: That's what I'm talkin' bout.